1. Field of Invention
The present invention relates generally to a facsimile optical scanning device and more particularly to an optical system for the high-speed scanning of X-ray film or similar translucent film.
2. Description of Prior Art
Several facsimile systems for scanning a document or film have been reduced to practice employing rotating or oscillating mirrors that sweep a beam of illuminating light passing through a stationary lens from side to side across the document or film. To accommodate the sweeping beam of illuminating light which is usually swept at a 15.degree. half angle, the stationary lens has to be a wide angle, large entrance pupil lens. Generally, the light beam is distorted at the ends of the sweep with a resulting loss of resolution and information, due to the varying focal lengths, aberrations and vignetting inherent in the optical system. At the expense of reduced optical efficiency, the size of the light beam is frequently limited to reduce aberrations and vignetting.
The focal length of the optical pat from the scanned line on the document or copy to the stationary or objective lens increases as the scan moves to the side of the document and the off center angle increases. The image on a fixed lens therefore goes out of focus. The W. Herriott patent, U.S. Pat. No. 2,262,584, entitled "Scanning Apparatus," which issued Nov. 11, 1941, shows a mechanism which moves one lens and a mirror to overcome the focus problem caused by the varying focal length.
As newer facsimile systems have been developed, it is not surprising that higher scanning speeds were sought. In such systems, it is known to illuminate a document by focusing a light source on a scanned element area through a condensing lens system while scanning the scanned element area with a second lens system which focuses a smaller portion of the scanned area as a real image upon a photoelectric cell. My patent, U.S. Pat. No. 2,894,064, entitled "High-Speed Facsimile Transmission System," which issued July 7, 1959, shows such a system. In this type of system, the light source, photoelectric cell and associated optics may be platform mounted and moved across the document as a single unit. While the resolution of such a system is acceptable, the scanning speed of such a system is still limited.